PROJECT SUMMARY Non-syndromic mitral valve prolapse (MVP), a common valvular heart disease affecting 2-3% of the human population, can lead to mitral regurgitation, cardiac dysfunction, congestive heart failure and even sudden death. Given the lack of medical therapeutics to manage this disease, MVP is currently treated by surgical intervention. Development of effective strategies for medical management has been hindered by an incomplete understanding of disease pathophysiology, specifically regarding factors that drive differentiation of valve interstitial cells (VICs) from fibroblast- to myofibroblast-like cells, resulting in myxomatous pathology. Furthermore, genetically modified animal models that faithfully recapitulate human MVP pathology are unavailable, in part due to the relative complexity of genetic factors found to be associated with disease predisposition. Interestingly, MVP (also termed myxomatous mitral valve degeneration) occurs frequently in dogs with an estimated incidence of greater than 50%. Previous comparisons of canine and human MVP demonstrated that they share several key histopathologic features suggesting that the spontaneous dog disease may represent a good translational model. Using canine MVP as a template, I have been investigating the potential role of extracellular vesicles (EVs) and miRNAs in driving the fibroblast to myoblast switch. EVs are membrane-bound cell-derived particles used for inter-cell signaling through the transfer of proteins and noncoding (nc)RNA, and they have been implicated in the propagation of several diseases including Alzheimer's and cancer. Our preliminary data show that canine VICs from diseased valves produce different cell-free miRNA and EV-associated ncRNA signatures than cells from normal valves. As such, the hypothesis underlying this proposal is that canine MVP can be leveraged to study EV-signaling mediated factors that drive myxomatous valve degeneration, with the ultimate goal of identifying and validating novel targets for early detection and therapeutic intervention. To accomplish this, I will first complete the characterization of canine MVP at the histopathologic and molecular levels with a direct comparison to human MVP, and then interrogate the impact of EV and ncRNA mediated signaling on VIC gene expression profiles and function. These data will facilitate a more complete understanding of how EV- mediated signaling influences the evolution of MVP and create a blueprint for incorporating spontaneous canine MVP into the translational pipeline to optimize novel approaches for early detection and intervention. The rich research environment at Tufts University and its partners including schools of Veterinary Medicine, Medicine, Nutrition and Graduate Sciences, Tufts Medical Center, the Tufts Clinical Translational Sciences Institute, and MIT ensure access to the resources and expertise necessary for successful completion of the proposed work. My training in engineering and medical cardiology combined with guidance from my mentoring team bridging expertise in human cardiology, comparative medicine, EV/ncRNA biology and bioinformatics/biostatistics makes me well positioned to successfully transition to an independent clinician-scientist.